1. Field of the Invention
This invention relates to a chemical treating apparatus and a flow rate controlling method thereof, particularly to a chemical treating apparatus used in the manufacturing process of semiconductor devices, especially in the cleaning process, and a flow rate controlling method thereof.
2. Description of the Prior Art
As it will be stated below, there are two methods for treating (cleaning, etching, etc.) the face surface or the back surface of a substrate such as a semiconductor substrate, a quartz substrate, and the like.
(a) One method of chemical treatment is using an overflow type chemical treating apparatus 101, as shown in FIG. 1, in which the subject of treatment (for example, semicondutor wafer, glass wafer, etc.) 131 is placed in a main bath 111, and a liquid treating chemical 121in (shown by an arrow) is supplied to the main bath 111 from its bottom portion while the liquid treating chemical 121out (shown by an arrow) in the main bath 111 is discharged from the top portion of the main bath 111 into an outer bath 112 provided on the top periphery of the main bath 111.
(b) The other method is using a down-flow type chemical treating apparatus 102, as shown in FIG. 2, in which the subject of treatment (for example, a semicondutor wafer, a glass wafer, etc.) 131 is placed in a main bath 111, and a liquid treating chemical 121in (shown by an arrow) is supplied to the main bath 111 from an outer bath 112 formed on the top periphery of the main bath 111 while the liquid treating chemical 121out (shown by an arrow) in the main bath 111 is discharged from the bottom portion of the main bath 111.
In each method mentioned above, a liquid treating chemical 121 is supplied to a main bath 111 storing the subject of treatment 131 while the liquid treating chemical 121 is discharged to the outside of the main bath 111, wherein the adopted flow rate of the liquid treating chemical supplied ranges widely from a very small quantity to several dozens dm.sup.3 /min. Generally, the optimum flow rate is set depending on the geometric shape of the main bath 111 and an outer bath 112, the subject of treatment 131 and the type of the liquid treating chemical 121 supplied. The set flow rate does not always have only one value; recent multi-functionalization in apparatuses has made it possible that more than one liquid treating chemicals are supplied alternately. In such a case, each time the type of liquid treating chemical is changed, the flow rate should be changed. Furthermore, even though apparatuses are designed so that the flow rate of a liquid treating chemical supplied is always constant during the supply, there are some cases where the flow rate variation during each supplying operation or the variation over a long time period exceeds a negligible level.
Further, in order to treat (for example, clean, wet-etch, etc.) the subject of treatment 131 uniformly, it is required that the liquid treating chemical 121 is sufficiently in contact with the face surface (or the back surface) of the subject of treatment 131 and that the liquid treating chemical 121 flows as laminar state as possible.
In the above-described overflow type chemical treating apparatus 101, regardless of the amount or variation of supply from the bottom portion of the main bath 111, the flow rate of the liquid treating chemical 121 in the main bath 111 is determined by the height of the wall of the main bath 111. Thus, unless the liquid treating chemical 121 is discharged from the main bath 111, the flow rate is stable irrespective of the amount of supply. Most of the conventional cleaning baths are overflow type ones which have such a structure that the liquid treating chemical 121 is supplied from the bottom portion of the main bath 111 and discharged to the outer bath 112. Therefore, the discharging capacity should be equivalent or exceed to the expected amount of supply. In addition, various discharging methods are applicable; that is, either the method using gravitation or the method using a pump is available. Therefore, variation of supply can be managed naturally by allowing the opening of the discharging port to have some extra area, for example.
On the other hand, in the above-mentioned down-flow type chemical treating apparatus 102, in order to keep the amount of the liquid treating chemical in the main bath 111 constant independent of the variation in the amount of supply of the liquid treating chemical 121 from the outer bath 112, it is necessary to discharge the same amount of the liquid treating chemical 121 as the amount of supply.